Variabilidade morfológica craniana de duas espécies de mamíferos neotropicais de ampla ocorrência geográfica, Herpailurus yagouaroundi (carnivora: felidae) e Galictis cuja (carnivora: mustelidae)

Abstract

The study of shape variation of organisms plays an important role in understanding a variety of biological processes, being one of the oldest subjects investigated in Evolutionary Biology. The geometric morphometric have been used to analyze variation in morphology, becoming a more quantitative science. For mammals the skull is one of the most informative structures used for studies. Morphometric analyzes of the skull of mammals from the order Carnivora with extensive distribution areas have shown that size and shape can vary by a wide range of factors. In this context, the wide geographical distribution and the wide range of habitats used by the jaguarundi, Herpailurus yagouaroundi, and the lesser grison, Galictis cuja, make them ideal species for investigations of variation of form. The objective of this work was to test two hypotheses: (I) populations of different ecoregions present localized phenotypes as adaptation to each environment; and (II) species present a more general phenotype along their geographic distributions, presenting differences according to the isolation by distance model. A total of 59 skulls of jaguarundis and 52 of lesser grisons were photographed in the ventral, dorsal and lateral views, all from adult individuals of known origin deposited in Brazilian museums. This material was analyzed using geometric morphometric techniques. The Student’s t-test showed significant sexual dimorphism in size for both species, with the male’s skull being larger than female’s. However, the multivariate analysis of variance did not detect sexual dimorphism in shape. The results showed that the individuals of jaguarundi are significantly larger in the Amazon region, while the lesser grisons from Uruguayan savanna are larger than the ones from the Atlantic Forest. Possibly these patterns are related to differences in the availability and size of resources of each ecoregion in relation to the others. The two species did not show significant differences in skull shape between the different ecoregions in Brazil, except for the lateral view of jaguarundi, which appears to present a localized phenotype in Cerrado. The distinct characteristics of this environment could be exerting selective pressures sufficient to distinguish these specimens. However, due to its ecological flexibility and scatter ability, and the high consistency of the skull shape of Felidae family to withstand certain morphological variability without losing functionality, this could be a fixed phenotypic fluctuation. The isolation by distance hypothesis was corroborated only for the lesser grison, due to the significant correlation between geographic distance and shape of dorsal view. However, the existence of localized phenotypes cannot be totally excluded due to the lack of sampling of specimens of this mustelid from other regions. This was the first work to investigate intraspecific variations in the skull shape and size of jaguarundi and lesser grison. Basic data on the ecology of both species are still needed in order to improve our understanding of the evolutionary processes involved. In addition, there is a lack of museological material in most of its distributions, especially the Caatinga and Cerrado ecoregions. Thus, samples that cover these environments, as well as more ecological studies are recommended to elucidate more accurately the nature and characteristic of the morphological, ecological and evolutionary variation of these species.